1. Field of the Invention
This invention relates to an optical pickup apparatus used in an optical disk apparatus so as to record and reproduce information relative to an optical disk medium such as a high-density disk and a compact disk. More specifically, the invention relates to an optical pickup apparatus in which an optical axis of an objective lens can be kept perpendicular to a recording surface of the optical disk.
2. Description of the Related Art
A conventional optical pickup apparatus will now be described with reference to FIG. 10. FIG. 10 is a perspective view of the conventional optical pickup apparatus, and FIGS. 11 to 14 are views explanatory of a skew of an objective lens developing when a conventional actuator device moves in a focusing direction and a tracking direction. More specifically, FIG. 11 is an enlarged view of a magnetic circuit portion, FIG. 12 is a cross-sectional view taken along the line Axe2x80x94A of FIG. 11, showing a tracking operation, FIG. 13 is a cross-sectional view taken along the line Axe2x80x94A of FIG. 11, showing a focusing-tracking operation, and FIG. 14 is a view explanatory of a skew of the pickup apparatus of FIG. 10 shown in FIG. 13.
As shown in FIG. 10, the conventional optical pickup apparatus comprises an objective lens 1 for converging light onto an optical disk, a lens holder 2 to which the objective lens 1 is secured by an adhesive or the like, a focusing coil 3 adhesively secured to the lens holder 2 so as to move the lens holder 2 in a focusing direction, tracking coils 4 adhesively secured to the lens holder 2 so as to move the lens holder 2 in a tracking direction, four wires 5 which serve to feed electric current to the focusing coil 3 and the tracking coils 4, and hold the lens holder 2 in a neutral position, relay boards 6 secured to the lens holder 2 by an adhesive or the like so as to relay the feeding of electric current to the focusing coil 3 and the tracking coils 4 from the wires 5, a suspension base 7 to which the four wires 5, holding the lens holder 2 in the neutral position, are fixedly secured, a yoke 9 fixedly secured to the suspension base 7 by an adhesive or screws, and magnets 8 fixedly secured to the yoke 9 by an adhesive or the like so as to impart a magnetic field to the focusing coil 3 and the tracking coils 4.
After an optical axis of the objective lens 1 is adjusted, the pickup apparatus of this construction is precisely fixedly secured to a carriage (not shown) by an adhesive or solder. By changing the magnitude and direction of electric current flowing through the focusing coil 3 and the tracking coils 4, the lens holder 2, holding the focusing coil 3 and the tracking coils 4, can be moved in a focusing direction and a tracking direction in accordance with Fleming""s left-hand rule.
With the above conventional actuator device, the lens holder 2 can be moved only in the two directions (i.e., the focusing direction and the tracking direction), and therefore when reading and writing information relative to an optical disk having a tilt, a skew angle (i.e., an angle between the optical axis and a line perpendicular to the disk surface) develops, which has resulted in a problem that the reading and writing become unstable.
Next, the focusing-tracking operation of the conventional pickup apparatus will be described. The behavior of the lens holder 2 will now be described with reference to FIG. 11D which is a cross-sectional view taken along the line Axe2x80x94A of FIG. 11A, showing the magnetic circuit and the focusing and tracking coils of FIG. 10. In FIGS. 12A, 12B, 13A and 13B, the showing of the lens-holder 2 is omitted since the behavior of the lens holder 2 can be shown by the focusing coil 3 and the tracking coils 4.
In FIG. 12A, the behavior of the lens holder 2 will be described, assuming that the direction of a magnetic field, formed by the magnets 8 and the yoke 9, is a direction from the front side of the sheet of the FIG. 12A to the rear side thereof. As shown in FIG. 12A, the direction of upward and downward movement of the lens holder 2 is the focusing direction whereas the direction of right and left movement of the lens holder 2 is the tracking direction. When electric current is flowed in the tracking coils 4 in directions of arrows (FIG. 12B), the lens holder 2 is moved left according to Fleming""s left-hand rule. Then, in this condition of FIG. 12B, when electric current is flowed in the focusing coil 3 in a direction of arrows (FIG. 13A), the lens holder 2 is moved upward in the focusing direction according to Fleming""s left-hand rule.
However, as a result of the movement in the focusing direction, the balance of the direction of the electric current in the focusing coil, existing in a magnetic field-existing region (indicated by hatching in FIG. 13B), is lost, and therefore the lens holder 2 is not moved parallel in the focusing direction, but is angularly moved in a counterclockwise direction to be skewed as shown in FIG. 13B. The amount of this skew increases as the amount of movement of the lens holder 2 in the focusing direction and the tracking direction increases. FIG. 14 is a view showing skew developing when the lens holder is moved in the focusing direction and the tracking direction.
The conventional optical pickup apparatus has the above construction, and therefore a tangential skew and a radial skew of the optical disk, which could be ignored in the conventional optical disk, can not be ignored in the recording and reproduction of a high-density optical disk in view of the reliability of a detection signal. For example, in a DVD, a dynamic skew margin is reduced in accordance with a short wavelength of a laser beam and a high NA (numerical aperture) of an optical system, and therefore a spindle motor for rotating the optical disk is skewed, or the skew is effected using a support shaft, supporting an optical pickup, and a guide shaft, and this adjustment margin prevents the achievement of the thin design. Non-standard optical disks have now been extensively marketed by various makers, and it has now become difficult to properly meet these various optical disks.
It is an object of this invention to provide an optical pickup apparatus in which there is provided simple drive means for controlling tilt of an objective lens relative to an optical disk, and the tilt control of an optical pickup is effected so that the optical axis of the objective lens can be kept perpendicular to a recording surface of the optical disk.
According to the present invention, there is provided an optical pickup apparatus comprising:
lens holding means holding an objective lens;
lens drive means for driving the lens holding means in a focusing direction and a tracking direction;
elastic support members fixedly secured at one ends thereof to the lens holding means to support the lens holding means in a manner to allow movement of the lens holding means; and
a support fixing member supporting and fixing the elastic support members, the other ends of the elastic support members being fixedly secured to the support fixing member;
wherein the lens drive means is disposed between the lens holding means and the support fixing member; and
wherein second lens drive means for driving the lens holding means in a direction inclined relative to the focusing direction or the tracking direction is provided between the lens drive means and the support fixing member.
The second lens drive means comprises magnets, mounted on the lens holding means, and coils mounted on the support fixing member.
With this construction, there can be provided the optical pickup apparatus in which the lens holding means can be dynamically tilted so that the optimum signal reading can always be effected, thus achieving the tilt adjustment, and the optical axis of the objective lens can be kept perpendicular to a recording surface of an optical disk.